1 udev - userspace device management
3 For more information see the files in the docs/ directory.
6 Integrating udev in the system has complex dependencies and differs from distro
7 to distro. All major distros depend on udev these days and the system may not
8 work without a properly installed version. The upstream udev project does not
9 recommend to replace a distro's udev installation with the upstream version.
12 - Version 2.6.19 of the Linux kernel for reliable operation of this release of
13 udev. The kernel may have a requirement on udev too, see Documentation/Changes
14 in the kernel source tree for the actual dependency.
16 - The kernel must have sysfs, unix domain sockets and networking enabled.
17 (unix domain sockets (CONFIG_UNIX) as a loadable kernel module may work,
18 but it does not make any sense - don't complain if anything goes wrong.)
20 - The proc filesystem must be mounted on /proc/, the sysfs filesystem must
21 be mounted at /sys/. No other locations are supported by udev.
25 Udev creates and removes device nodes in /dev/, based on events the kernel
26 sends out on device discovery or removal.
28 - Very early in the boot process, the /dev/ directory should get a 'tmpfs'
29 filesystem mounted, which is populated from scratch by udev. Created nodes
30 or changed permissions will not survive a reboot, which is intentional.
32 - The content of /lib/udev/devices/ directory which contains the nodes,
33 symlinks and directories, which are always expected to be in /dev, should
34 be copied over to the tmpfs mounted /dev, to provide the required nodes
35 to initialize udev and continue booting.
37 - The old hotplug helper /sbin/hotplug should be disabled on bootup, before
38 actions like loading kernel modules are taken, which may cause a lot of
41 - The udevd daemon must be started on bootup to receive netlink uevents
42 from the kernel driver core.
44 - All kernel events are matched against a set of specified rules in
45 /lib/udev/rules.d/ which make it possible to hook into the event
46 processing to load required kernel modules and setup devices. For all
47 devices the kernel exports a major/minor number, udev will create a
48 device node with the default kernel name, or the one specified by a
51 Please direct any comment/question/concern to the linux-hotplug mailing list at:
52 linux-hotplug@vger.kernel.org